1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has two side shields.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density when compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on the top surface of a substrate. The write head unit includes a main pole configured to produce a write magnetic field in the direction perpendicular to the plane of the recording medium. The main pole has an end face that is located in a medium facing surface configured to face the recording medium.
The main pole includes, for example, a track width defining portion having an end located in the medium facing surface, and a wide portion connected to the other end of the track width defining portion. The track width defining portion has a top surface having a width smaller than that of the top surface of the wide portion. The width of the top surface of the track width defining portion in the medium facing surface defines the track width. To achieve higher recording densities, the track width should be as small as possible. Here, the length of the track width defining portion in the direction perpendicular to the medium facing surface will be referred to as the neck height. To improve the write characteristics of the write head unit, such as the overwrite property which indicates the overwriting capability, the neck height should be as small as possible.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically in the form of a slider. The slider has the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the leading end into the space between the medium facing surface and the recording medium.
Here, the side of the positions closer to the leading end relative to a reference position will be defined as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs depending on the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew can cause the phenomenon that signals already written on one or more tracks in the neighborhood of a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. Unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording densities, it is necessary to prevent unwanted erasure.
A known technique for preventing unwanted erasure induced by the skew is to shape the main pole such that its end face located in the medium facing surface has a width that decreases with increasing proximity to the top surface of the substrate, as disclosed in U.S. Pat. Nos. 8,270,110 B2 and 8,289,649 B2, for example.
U.S. Pat. Nos. 8,270,110 B2 and 8,289,649 B2 also disclose other effective techniques for preventing unwanted erasure induced by the skew. One of such techniques is to provide two side shields on opposite sides of the main pole in the track width direction, and another one is to provide a shield having an end face that is located in the medium facing surface and wraps around the end face of the main pole (such a shield will hereinafter be referred to as a wrap-around shield). The wrap-around shield includes a bottom shield located on the air-inflow-end side relative to the main pole, a top shield located on the air-outflow-end side relative to the main pole, and two side shields located on opposite sides of the main pole in the track width direction. These techniques allow for capturing a magnetic flux that is produced from the end face of the main pole and spreads in the track width direction. Thus, the occurrence of unwanted erasure can be prevented by these techniques.
A main pole of such a shape that its end face located in the medium facing surface has a width that decreases with increasing proximity to the top surface of the substrate suffers a problem as described below. If a main pole of such a shape is formed by a conventional method of forming a main pole, major part of the side surface of the main pole along the entire perimeter of the main pole will be formed into a slope inclined relative to a direction perpendicular to the top surface of the substrate. In such a case, the main pole has a smaller cross-sectional area perpendicular to the direction in which magnetic flux flows, when compared with a case where the entire side surface of the main pole is perpendicular to the top surface of the substrate. The main pole of the foregoing shape is unable to allow much magnetic flux to pass therethrough, especially through a portion near the boundary between the track width defining portion and the wide portion wider than the track width defining portion, and as a result, will cause degradation of write characteristics such as overwrite property.
An effective technique for solving the foregoing problem is, as disclosed in U.S. Pat. No. 8,289,649 B2, to form the main pole into the following particular shape. The main pole formed by the technique disclosed therein has six side surfaces: first and second side surfaces that are opposite to each other and located in a first region extending from the medium facing surface to a position at a predetermined distance from the medium facing surface; third and fourth side surfaces that are located in a second region other than the first region; a fifth side surface located in the boundary between the first and second regions and connecting the first side surface and the third side surface; and a sixth side surface located in the boundary between the first and second regions and connecting the second side surface and the fourth side surface. The distance between the first side surface and the second side surface in the track width direction decreases with increasing proximity to the top surface of the substrate. In the boundary between the first region and the second region, the distance between the third side surface and the fourth side surface in the track width direction when seen at the position closest to the top surface of the substrate is greater than the distance between the first side surface and the second side surface in the track width direction when seen at the position closest to the top surface of the substrate. Each of the fifth and sixth side surfaces has a width that increases with increasing proximity to the top surface of the substrate. This technique allows the main pole to have a large cross-sectional area perpendicular to the direction of flow of magnetic flux in the vicinity of the boundary between the track width defining portion and the wide portion, so that much magnetic flux can pass therethrough. This makes it possible to improve the write characteristics such as the overwrite property.
In the magnetic head disclosed in U.S. Pat. No. 8,289,649 B2, the distance between two main-pole-facing sidewalls of the two side shields gradually increases with increasing distance from the medium facing surface. In this structure, the cross-sectional area of the main pole in the vicinity of the medium facing surface is limited by the distance between the aforementioned two sidewalls of the two side shields. This structure thus has the drawback of being unable to sufficiently increase the cross-sectional area of the main pole in the vicinity of the medium facing surface.